DESCRIPTION (applicant's abstract): Because early hormonal exposure, whether endogenous or exogenous, may have long-lasting effects on the behavior of an organism, such as maturation, reproduction, and cognition, it is important to understand these changes. The presence of maternal hormones in vertebrate eggs suggest a hormonal link between the mother and the offspring which may allow the mother to differentially influence offspring fitness. The present proposal is designed to specifically investigate the role of maternal androgens in the organization of the developing brain and the effects on behavior using the house sparrow, Passer domesticus, as our working model. Our hypothesis is that maternal hormones deposited in variable amounts in the avian egg influence brain differentiation during development leading to differences in behavior among siblings and broods of birds. Using radioimmunoassays to measure androgen levels, and immunocytochemistry in in situ hybridization to detect androgen receptors, this study will examine the ontogeny of behavioral differences relating to individual fitness. This study is unique in that it will examine individual variation at multiple levels. In addition to neuronal differences, I will also be examining hormone levels, physiology (weight, plumage) and behavior (aggression, courtship, reproduction & cognition) to determine if variable amounts of maternal hormones provide a selective advantage to specific individuals.